1. Field of the Invention
The invention relates to a grease composition comprising a lubricating oil and a polyurea thickener and a process for its preparation. More specifically, the polyurea thickener is the reaction product of a diisocyanate, a monoamine and a low molecular weight polyoxyalkylene diamine.
2. Description of Related Information
Polyurea thickened grease compositions are used commercially to provide lubrication at high temperature for extended periods of time. The polyurea thickening agents are typically formed by reacting an isocyanate with an amine mixture in a base oil to yield the polyurea grease composition.
For example, U.S. Pat. No. 4,661,276 discloses a grease composition comprising a major amount of a lubricating oil base vehicle a polyurea gellant and a minor amount of a polymer having a pKa value of greater than 5.0.
U.S. Pat. No. 5,238,589 discloses a grease composition comprising a lubricating oil and a polyurea thickener prepared by reacting a diisocyanate compound with a monoamine, a diamine and a selected copolymer. The copolymer can be a polyoxyethylene/polyoxypropylene diamine copolymer with a molecular weight of 500 to 18,000.
U.S. Pat. No. 4,261,845 discloses a grease composition using polyureas prepared by reacting an alkylpolyalkoxy monoamine with an organic polyisocyanate.
U.S. Pat. No. 3,879,305 discloses a grease composition containing a thickening agent comprising a polyurea prepared by reacting a monoamine, a diisocyanate and a diamine having one amino group attached to each of two hydrocarbyl groups and the hydrocarbyl groups being separated by an oxygen or sulfur atom. The examples disclose greases having NLGI Grade No. 2 hardness at approx. 12% thickener levels.
I have discovered that by reacting a low molecular weight polyoxyalkylene diamine with a monoamine and a diisocyanate, a grease with an improved yield (low penetration number vs. high) is obtained when compared with greases thickened with other amine mixtures. A harder grease (NLGI Grade No. 3) is produced as opposed to a softer grease (NLGI Grade Nos. 2 or 1) which results when higher molecular weight polyoxyalkylene diamines or alkylene diamines are used.
The polyurea thickener of the present invention is a more effective thickener system than prior thickener. The polyurea thickener of the present invention allows the production of softer greases, i.e., NLGI Grades 1 and 2, more economically due to its superior thickening ability.